1. Field of the Invention
The present invention relates to a technique for removing an unnecessary coating film at an edge portion, for example, of a substrate having a coating film formed thereon.
2. Description of the Background Art
In a manufacturing process of semiconductor devices and LCD substrates, a resist pattern is formed on a substrate by a technique called photolithography. This technique is performed, for example, through a series of steps of applying a resist liquid on a substrate such as a semiconductor wafer (referred to as a wafer hereinafter), exposing the resist in a prescribed pattern, and thereafter performing a development process to obtain a desired pattern. Such a process is generally performed using a system in which an exposure apparatus is connected to a coating and developing apparatus for applying and developing a resist liquid.
Recently, as device patterns are increasingly reduced in size and film thickness, there is a growing demand for increasing the resolution of exposure. Then, for example, an approach of performing exposure with a light-transmitting liquid layer formed on a surface of a substrate (referred to as “liquid immersion exposure) has been developed by further improving exposure techniques using argon fluoride (ArF) or krypton fluoride (KrF) to increase the resolution. This liquid immersion exposure is a technique of, for example, allowing light to pass through pure water, and utilizes such a characteristic in that an optical wavelength is shorter in water and thus the wavelength of ArF of 193 nm is substantially 134 nm in water.
On the other hand, edge rinse for removing a resist film at an edge portion outside of a circuit formation region of a wafer has conventionally been performed after application of a resist liquid. The edge portion of the wafer has a beveled structure in order to be held by a transport arm. If a resist film is present here, the resist film adheres to the transport arm and then peels off from the transport arm in a transport step, resulting in particles which are a cause of defects. The particles scattering in the apparatus or being transferred to another wafer W become a factor contributing to particle contamination.
The aforementioned edge rinse is performed, for example, as shown in FIG. 13A, by applying a resist liquid on a surface of a wafer 10 to form a resist film 11, and thereafter discharging an organic solvent such as thinner from a nozzle 12 toward an edge portion of wafer 10. As disclosed in Japanese Patent Laying-Open No. 2001-110712, a coating film removing apparatus dedicated for an edge rinse step may be used for removing an unnecessary coating film at the edge portion of a wafer at high accuracy.
However, in the edge rinse using an organic solvent, because of the compatibility between organic solvents and coating films, with some kinds of resist film, it is difficult to sharply cut the resist film at the edge portion of the wafer in such a manner in that the end portion is linearly shaped. For example, as shown in FIG. 13B, because of the presence of a part 13 where the resist film rises like a knot or a part 14 where the dissolved component of the resist film drips into a region to be removed so that the resist film is left thinly in the vicinity of the outer edge of the wafer, the resist film is often cut bluntly. In particular, since the edge portion of wafer W has a beveled structure, the resist film is hardly removed and may remain on the inclined surface at the edge portion of wafer W.
In this state, in the liquid immersion exposure process as mentioned above, as shown in FIG. 13C, since the process is performed by moving an exposure portion 15 in a state in which wafer 10 and exposure portion 15 are in contact with each other with water 16 interposed therebetween, the presence of knot-like part 13 changes the water flow and the effect during movement of exposure portion 15, which may cause a phenomenon in which the resist film peels off from wafer 10. In addition, water 16 intrudes by capillarity between from wafer W and resist film 11 thinly left in the vicinity of the outer edge of the wafer, which may cause peeling of resist film 11, as shown in FIG. 13D. Moreover, for example, in a case where a plurality of coating films are stacked, for example, where an antireflection film is formed under resist film 11, water 16 easily intrudes in the neighborhood of the boundary between the antireflection film and resist film 11, and film peeling from that region may occur. It is reported that a coating film such as resist film 11, which peels off at the time of liquid immersion exposure process in this manner, attaches to wafer 10 again and is detected as a defect.
In the edge rinse using an organic solvent, because of the compatibility between the resist liquid and the organic solvent as described above, the accuracy of cut width of a film to be removed is deteriorated or the shape of the cut surface is deteriorated. In addition, for example, in the case where a plurality of coating films are stacked, for example, where an antireflection film is formed under the resist film, edge rinse of the underlying coating film is performed before the overlying coating film is formed. Therefore, in the underlying coating film, the cut width has to be set with allowance for the overlying coating film to be formed and thus a larger cut-width margin has to be set. As a result, the cut width becomes greater, and it is likely that the circuit formation region of wafer 10 is reduced accordingly.
Here, as a technique of removing the unnecessary resist film at the edge portion of the wafer, an edge exposure process may be performed. In this edge exposure, an exposure process is selectively performed on the unnecessary resist film at the edge portion of the wafer before an exposure process, for the purpose of removing the unnecessary resist film at the edge portion in the subsequent development step. According to this technique, since the resist film at the edge portion is optically removed, advantageously, the unnecessary resist film can be removed sharply in such a manner that the end portion is shaped linearly. However, since the unnecessary resist film at the edge portion cannot be removed without a development process after the exposure process, the resist film may attach to a transport arm and cause particles in the transport step before the development process, as described above. In addition, in the liquid immersion exposure process, the resist film present at the edge portion of the wafer comes in contact with water, which may cause film peeling.
In the above-noted Japanese Patent Laying-Open No. 2001-110712, an unnecessary coating film formed at the edge portion of a wafer is removed at high accuracy by positioning a rinsing liquid ejection portion based on detection of an outer edge position of a substrate. With the configuration of Japanese Patent Laying-Open No. 2001-110712, peeling of the resist film from wafer 10 in the liquid immersion exposure process cannot be solved.